Radio antenna



A g- 30, 1949. E. o. WILLOUGHBY RADIO ANTENNA 2 Sheets-Sheet 1 FiledJan. 16, 1945 'INVENTOR. 5% 0550/P/VE Maw/my 2 Sheets-Shet 2 IN VEN TOR.

ATTORNEY Aug- 30, 1 E. o. WILLOUGH'BY RADIO ANTENNA Filed Jan. 16, 1945rll 1 $5.52!

Patented Aug. 30, 1949 RADIO ANTENNA Eric Osborne Willoughby,

signer, by mesne assignments, St'and'ard'Electr-ic Corporation, acorporation of Delaware London, England, asto International New York, N.Y.,

Application January 16, 1945', Serial No; 573,099 In Great BritainNovember 5, 1943 Section 1, Public Law 690, August 8, 1946 PatentexpiresNovember 1963 8 Claims. (Cl. 250*33) The present invention relates toradio antenna systems and it has for its chief object to provide anantenna system for use at ultra high frequencies, for example 100-150megacycles which has a substantially flat amplitude-frequencycharacte'ri'stic over a wide frequency band of the order or 20% of themean fre uency on either side of said mean frequency.

According to one aspect of the invention an antenna system having asubstantially constant resistance over a broad operating band of ultrahigh fre'qu'en'c'ies includes an antenna comprising a hollow conductingcylinder erected vertically above the ground but insulated from it andhavinga physical length between one quarter and one half the meanoperating wave length, and half wave resonant at the mean operatingfrequency, a central conductor which passes through said hollow cylinderto form therewith a stub and means for tuning the said stub to resonanceat the mean operating frequency, a transmission line preferably screenedfor coupling said antenna to a translation device and a quarter waveline im: pedance transformer at substantially said mean frequencycoupling said antenna and said transline.

According to another aspect of the invention a dipole radio antennasystem having a substantially constant resistance over a broadoperatingband of ultra high frequencies includes a dipoleantennacomprising two hollow conducting cylinders each having aphysical lengthbetween one quarter and one half the mean operating wave length, andhalf wave resonant at the mean operating frequency, central conductorswhich pass through the respective hollow cylinders forming stubstherewith and means for tuning said stubs to resonance at the meanoperating frequency, a transmission line preferably screened forcoupling the antenna to a translation device, and a quarter wave lineimpedance transformer at substantially said mean frequency coupling saidantenna and" said transmission line.

The lower end of the vertical antenna is prefer ably conical and taperstowards the ground and the inner ends of the dipole cylindrical membersare preferably conical tapering towards each other, and the physicallength of the vertical antenna, or each of the dipole members tuned tohalf waveresonance is between one quarter and one half the meanoperating wave length.

An antenna embodying the invention is effectively fed; from the conicalend; since the waves pass down the inside of the cylinders from thecylindrical end and along" the outside of the cylinder from the conicalend during the radiating' action. In a receiving antenna the reverseaction takes lace.

The characteristic impedance of the conical portion of the antenna ispreferably of the same order asthe characteristic impedance of thecylindrical portion, the chief purpose of the conical endbeihg to avoidthe capacity irregu-= larity present with ends of large cross-sectionscoming close together at the feed point and to provide a smooth feedintothe e'ifective portion of the antenna system free from excessive shuntcapacity e'fs'e'ctsl A An antenna of low characteristic impedance isemployed thereby keeping the end radiation resistance' low and atransmission line of relatively high characteristic impedance(particularly if ascre'ene'd" line-is desired) is employed to reduce theimpedance transformation ratio in order that a quarter wave lineimpedance transformer may we used for coupling the antenna andtransmission line. The antenna is series tuned throughout the frequencyband by using series tuned elements of appropriate value in series withthe antenna thus taking advantage of} the fact that the reactance of ahalf wave antenna varies in the opposite direction with frequencythrough resonance as does a series tuned circuit consisting of seriesconnected inductance" and capacity.

The series tuning of the antenna throughout the frequency band canbecarried out sufficiently well that the antenna may be considered as asubstantially ure resistancevarying with frequencyac'cofding' to a lawrepresented by a smooth curve with-the maximum near the centre of theoperating band substantially twice as high as that on the extremes ofthe operating band, and the problem of coupling tlie'an'tenna to atransmission line then resolves itself into matching the characteristicimpedance of the transmission line with that of the said pure resistancvarying in the manner stated.

If Z9 is the characteristic impedance of the reed line, a quarter waveimpedance matching transformer whose impedance is /R,Zo where R istliemean resistance of the antenna over the frequency band, gives animpedance mismatch between the antenna and line of the order 5:4, i.- e.o'fthe order of 0.2 db. Such a coupling unit is compact and'by slightover-compensation of the antenna as seen at its reaetance of thehalf-wave base, the s'm'all' reactance-introduced by deviation ofthematcfiing transformer from quarter wavelength-in the tuning band'lcanbe largely compensated'; By overcompensation is meant introducing agreater series reactance than is required for neutralisation of theantenna reactance 1n the operating frequency band. Such a quarter waveline coupling impedance transformer is thus suitable for coupling theantenna and a screened transmission line. With a coupling unit of thistype the losses at the extremes of the frequency band are smaller thelower the impedance transformation ratio.

Such a coupling unit has also mechanical advantages since it isextremely compact, rigid, and simple, and can be carried with theantenna at the end of a long length of transmission line, whereas a moretheoretically perfect coupling unit involves a plurality of condensersand inductances and is complicated and voluminous, and its superiorityin performance over the simple quarter wave transmission line is small.

trical contact therewith and through the bushing 6 so that it can bemanipulated to adjust the q capacity and at the same time connect thecondenser across the tube.

The condenser at the same time series tunes the lower open end of thestub to the mean operating frequency and thus makes the impedance acrossthe open or lower end of the stub or antenna zero at the mean operatingfrequency.

-The location of this condenser may be used 7 to make the reactancecharacteristic across the open end of the stub vary unsymmetrically withThe accompanying drawings show by Way of example some practicalembodiments of the invention.

In the drawings, Figure 1 shows an antenna system according to theinvention utilising an unbalanced antenna with respect to earthpotential.

' Figure '2 shows an antenna system according to the invention utilisinga dipole or balanced antenna and transversely arranged transmissionline.

Figure 3shows a supporting arrangement for the antenna system shown inFigure 2.

Figures 4, 5 and 6 show a dipole antenna system according to theinvention with the-transmission line coaxial with the dipole antenna.Figures 5 and 6' are partial views showing modified connections for usewith a concentric and twowire transmission line respectively.

Figures '7 and 8 show supporting arrangements for the antennasystems ofthe type shown in Figures 4, 5 and 6.

In all the figures like reference characters.

Referring to Figure 1,- the reference numeral I indicates the hollowconducting cylinder which is closed at its upper end 2 and has a conicallower end 3 tapering towards the ground or earth plane indicated at 4.The antenna is enclosed in an insulating tubular casing 5 and held inposition therein by means of asupporting bushing 6, for example, ofpolystyrene located substantially at the voltage node on the cylinder Iand this tubular'casing is supported directly on the earth plate 4 butholds the antenna I insulated from the ground. The central conductor isshown at 1 its upper end to the closed end 2 of the hollowconducting'eylinder I, and passes through the lower conical end atwhich, if necessary, a low capacity centring insulator may be used; 8indicates the transmission line for connection to a translating device.The quarterwave line impedance transformer is. indicated at H)connecting the transmission line 8 to the antenna I.

The cylindrical hollow conductor I has a physical length of less thanhalf the mean operating wavelength. The central conductor 1 togetherwith the hollow conductor I closed at its upper end forms a shortcircuited stub having an electrical length between one-quarter andone-half the mean operating wavelength. This stub is tuned to resonanceat substantially the mean frequency of the operating band by paralleltuning the upper closed end of the stub by means of an adjustablecondenser I I accommodated within the. hollow cylindricalmember I andconnected parts are given the same frequency about the mean operatingfrequency to an extent that matches the unsymmetrical reactancecharacteristic of the antenna with respect to the mean operatingfrequency.

The characteristic impedance of the stub is chosen for example, bysuitable diameter of the central conductor so that the reactance seenacross its open end is equal and opposite to the reactance at the baseof the antenna, that is, of the hollow cylindrical member alone, atfrequencies near the outer limits of the operating frequency band.

Actually a single open wire line a quarter of the mean operating wavelength long or an open stub and tuned to quarter wave series resonanceat the mean operating frequency in the cylinder will couple the antennato the transmission line and give a good degree of reactancecompensation, but the reactance changes obtainable by this means are notso great as in the preferred form shown in Fig. 2. 7 Also the circuitconstants are inconvenient in value and the system is not sosatisfactory mechanically as the preferred form.

The insulating casing 5 provides a weather screened space around theantenna and weather conditions have a reduced and more uniform effect onthe performance of the antenna over the operating frequency band thanone which is not screened.

,It should be noted that the single matching transformer I0 may bereplaced by two matching transformers in series of characteristicimpedances ZI and Z2 respectively such that R, Zl, /ZIZ2, Z2, and Z0 arein geometrical progression, where R is the mean resistance of theantenna, and Z0 is the characteristic impedance of the transmissionline. This arrangement would provide a slight improvement in performanceover the single transformer.

Referring now to Figure 2 a dipole antenna comprises two members asdescribed in connection with Figure I placed with their conical ends 3-,S'adjacent each other and the transmission line comprises two coaxialtransmission lines, but may be a two wire screened transmission line,brought horizontally to the two conical ends of the hollow conductingcylinders and. each is coupled to its respective central conductor 1, 1'of the two members through a quarter wave line impedance transformer I0;I 0' of suitable characteristic impedance as described in connectionwith Figure 1. (It should be understood that screened lines are hererecommended'for ease of mounting in such cases as ship installations butan unscreened balanced transmission line may be used.)

The two dielectric cylinders 5, 5

m e sea isogwa cured together; and: the antenna suspended: th'ere-.

byfrom aguy wire. I23. asshowir-in Figure 31 or maybesecuredt'o thetopofi awoodenm'ast.

A smallilen'gth I141of'conductor may be allowed" between thecouplingtransformer- L: and the central conductor 1: (Fig. l=) or conductors T,i. (Fig. 2) as it will compensate for some displacement of the meantuning condenser from the optimum position which displacement itself:effects compensation for the unsymmetrical antenna.reactancecharacteristic;

The balanced: or twovwire-screened transmisquired on the outer screen ofthe transmission line. This latter feature is of great value when the:antenna: is to operate over a wide frequency band and renders the dipoleantenna describedthe simplest and'best balanced antenna in, regard toperformance throughout the operating' nequency-band.

It ispossible to feed the dipole antenna by means of a single,unbalanced. transmission line, but due to a larger impedancetransformation ratio, an; increase of; approximately 0.1 db. in. the

mismatch at the extremes of thefrequency band will occuranditisunecessary to use a standing wave suppressor on the outside ofthe transmission: line.

When thedipole antennaiis-ifedzby a transmissien line in;alignmentwithzthe antenna as shown in Figures4, 5..and.6.(ratherthan'transverse-to the, dipole as. shown in. Figure 2E)- the couplingimpedance transformer liiis accommodated withinlthecylindrical.memberintoiwhich the line is taken, that: is.the lower. oneas shown in Figures 4, 5- and 6; so that. the formerly closed lower endis now open and=it is, necessary to put a short circuit between theouter conductor of the quarter wave: line impedance-transformer and thehollow cylindrical-member at-suc-h a distance from the open conical endof the cylindrical member to form a quarter wave closed stub at the meanoperating frequency in order to suppress standing waves on the saidouter conductor of the impedance transformer and transmission line. Thisshort circuit is shown as a conducting disc l5 having a central aperturefor the passage of the central conductor.

The central conductors of the quarter wave line transformer where aconcentric line is used (Figs. 4 and 6) or one of the conductors of atwo wire line (Fig. 5) is connected to the central conductor I of theupper cylindrical member. In the case of the two wire line (Fig. 5) theother wire is connected to the outside of the lower cylindrical member Ias shown at 16 and in the case of the coaxial line (Figs. 4 and 6) theouter conductor of the quarter wave line transformer is connected to theapex of the conical end of the lower cylindrical member I as shown at I1(Figs. 4 and 6).

In regard to suppressing the standing Waves on the outer conductor orscreen of the transmission line a low characteristic impedance antennais an advantage as it allows a relatively high impedance suppressingstub to be constructed. As a refinement it may be beneficial to 6.conneotxsuppresson" stubs tunedztoa and inequen'ciesof; the frequencybandiatpositions along the fee'ddinedetermined:experimentally, butsimplicity would probably dictate-a compromise such.

. as can be obtained with a. quarter wave. suppressing stub. ofrelatively highimpedance together with some small increase in loss atthe extremes of the operating frequenc'y band; Thisstub is formed by theshortcircuit device I5 betweenthe cylinder I? and the quarter wave-finpedanc'e-trainsformer I 0; thus providi-ng aquar ter wave blocking stubon the outer conductor of a transmission line.

In the case of the unbalanced transn-i-i'ssion' line Figs. 4-and-6 theouter concentric conductorof the line is terminated on the lowerhalf-waveantennamember i; but thecase of atwo: Wire transmission line; atuning capacity as indicated at lain Figure-Sis necessary topa-rallel'tune the short oi-rcuited stub, formed by" theshort circuit disc t5 theouter screenconductor o'f the quarter wave line impedance transformerand the'inside of the'antenna lower cylindrical memher I. To keep theresistance frequency re-- sponse characteristic as fi'at-aspo'ssible',the short circuiting device the form of adisc annulus, should lee-thinand a relatively low. character istic impedance antenna usedso' that thei-mr pedance of the blocking stub will benign.

shown" in Figure 7- the antenna with the transmission line coaxialtherewith may be supported-iroma=guy wii=e=-l3 or as shown in'Fig. 8"may be supportedonthetop of the wooden mast '9;

What is-claimed-is:

l; A radio antenna system hmiing a' substantially constantresistance-over a broad operating band of \ultrahigh frequenciesincluding anan.- tenna comprising a liollow'conducting" cylinderhaving'a physical length' between one quarter'and one half the meanoperating wavelength and half wave resonant at the meanoperating' fre'-quency, a central conductor which extends through the length of saidhollow cylinder and is connected-to one end thereof to form therewith ashort circuited stub, a reactance element connected'between' saidcentral conductor and said cylinder at a point intermediate the endsthereof for =tuning'said' stub" to resonance at the. mean operatingfrequency; a transmission line for coupling said antenna to atranslation device and an impedance transformer substantially a quarterwave length of said mean frequency coupling the open circuited end ofsaid antenna and said transmission line.

2. A dipole radio antenna system having a substantially constantresistance over a broad operating band of ultra high frequenciesincluding a dipole antenna comprising two hollow con ducting cylinderseach having a physical length between one quarter and one half the meanoperating wave length and half wave resonant at the mean operatingfrequency, a central conductor which extends through the length of oneof said hollow cylinders and is connected to one end thereof forming astub therewith, a central conductor which extends through the length ofthe other of said hollow cylinders and connects with the inner side ofsaid cylinder forming a stub therewith, a reactance element connectedbetween said central conductor and said cylinder at a point intermediatethe ends thereof for tuning said stubs to resonance at the meanoperating frequency, a transmission line for coupling the antenna to atranslation device and an impedance transformer substantially aquarterwave length of said mean frequency coupling the open circuitedend of said antenna and said transmission line,

3. A radio antenna system; having a substantially constant resistanceover a broad operating band of ultra-high-frequencies including anantenna comprising a hollow conducting cylinder having a physical lengthbetween one-quarter andone-half of the mean operating wavelength andhalf wave resonant at the mean operating frequency, a central conductorextending through said hollow cylinder connected to one end thereof andforming therewith a, stub, the outer end of said vertical cylinder beingclosed, said cylinder having a reactance element connected between saidcentral conductor and said hollow cylinder at a point intermediate theends thereof for parallel tuning to resonance at the mean frequency.

of operation a length of the cylinder and central conductor not greaterthan one-quarter of the mean operating wavelength from the closed end,said reactance element also series tuning the other portion of saidcylinder and central conductor to substantially the mean frequency andforming a quarter wave stub of said other portion, thereby making theimpedance across the open end of the stub substantially zero at the meanoperating frequency; a transmission line for coupling said antenna to atranslation device and a quarter wave line impedance transformer atsubstantially said mean frequency coupling said antenna and saidtransmission line.

4. A radio antenna system as claimed in claim 3, said reactance elementcomprising an adjustable capacity connected across the said cylinder andthe central conductor. 7

5. A dipole antenna system having a substantially constant resistanceover a broad operat ing band of ultra-high frequenciesincluding a dipoleantenna comprising two hollow conducting cylinders each having aphysical length between one quarter and one half the mean operatin gwave length and half wave resonant at the mean operating frequency, twocentral conductors, one extending through the length of each of saidhollow cylinders and connected to the ends thereof to form a shortcircuited stub therewith and two reactance elements; one being connectedbetween each of said central conductors and said cylinders at a pointintermediate the ends thereof for tuning said stubs to resonance at themeanoperating frequency, a transmission linefor coupling said antenna toa translation device and an impedance transformer substantially aquarter 5 wave length of said mean frequency coupling the open circultedend of said antenna and said trans-- transformer being accommodatedwithin one of said conducting cylinders and further including means forsuppressing standing waves on the transmission line.

8. A radio dipole antenna system as'claimed claim '7, said meanscomprising a short circuiting conductor between the screen of saidbalanced transmission line and said one cylinder at substantially aquarter of the mean operating wave length from the inner end of saidcylinder.

ER1C OSBORNE WILLOUGHBY.

REFERENCES CITED The following references file of this patent:

are of record in the UNITED STATES PATENTS Number Name Date 2,067,337Polatzek Jan. 12, 1937 2,158,271 Buschbeck May '16, 1939 40 2,167,709Cork Aug. 1, 1939 2,226,686 Alford Dec. 31, 1940 2,239,700 Carter Apr.29, 1941 2,311,364 Buschbeck Feb. 16, 1943 2,321,454 Brown June 8, 19432,368,298 Harris Jan. 30, 1945 FOREIGN PATENTS Number Country Date878,564 France Jan. 25, 1943 260,005 Great Britain Mar. 24, 1927 7. Aradio dipole antenna system as claimed in claim 2, in which thetransmission line is screenedand approaches the dipole antenna along thelongitudinal axis of the antenna, said impedance

